1. Field of the Invention
The present invention relates to an image forming apparatus that prints image data including a color code symbol, and more particularly to a technique for printing a code symbol.
2. Description of the Related Art
There has been proposed a technique of printing a geometric figure corresponding to coded information in addition to characters and images on a recording medium to thereby embed the coded information in a printout. Well-know examples of the geometric figure corresponding to coded information include a bar code and a QR code (registered trademark).
Further, the recording medium is not limited to a physical medium, such as paper, but by embedding a code symbol in electronic image data, it is also possible to perform embedding of information.
Further, a bar code in colors or in the form of a two-dimensional code makes it possible to encode an increased amount of information. As a consequence, by encoding an image or audio data, or by encoding data of an original image, it is possible to copy an image without deteriorating the image, and further, by encoding security information, it is also possible to inhibit copying of documents (see e.g. Japanese Patent Laid-Open Publication No. H10-055420).
When an image is printed by reading from an original, there are cases where it is required to print a code symbol in single black color depending on user setting or the type of an apparatus used for printing. More specifically, there are, for example, a case where a user has selected printing in a monochrome mode even though a printer capable of performing color printing is used, and a case where the printer is a monochrome printer incapable of performing color printing. In such cases, an image of a color code symbol (color code) is printed as a halftone image in single black color, but it is technically difficult to reproduce the code symbol in single black color without losing information held in the color code at the time of printing.
As described above, if a color code is copied in monochrome, information held in the color code is lost. This brings about a problem that information cannot be acquired from the code symbol copied on the sheet, and a problem that a function using the information held in the color code (e.g. a function of inhibiting copying for security purposes) becomes unavailable.
Further, there has been proposed a method in which when storing image data read from a color original in a hard disk, the data is stored as monochrome image data so as to reduce the amount of data to be stored. In such a case as well, similarly to the above, a color code is changed into monochrome image data, and hence information held on the original in the color code is sometimes lost.